This is the most basic and extensive application field of PLC. It replaces the traditional relay circuit to realize logic control and sequence control. It can be used for single machine control, multi-machine group control and automatic production line. Such as injection molding machine, printing machine, stapler, modular machine tool, grinder, packaging production line, electroplating production line, etc.

2. Analog control

In the process of industrial production, there are many continuously changing quantities, such as temperature, pressure, flow, liquid level and speed, which are all analog quantities. In order to make the programmable controller deal with analog quantity, it is necessary to realize A/D conversion and D/A conversion between analog quantity and digital quantity. PLC manufacturers all produce matching A/D and D/A conversion modules, so that programmable controllers can be used for analog control.

3. Motion control

PLC can be used to control circular motion or linear motion. From the configuration of control mechanism, I/O module was used to directly connect the position sensor and actuator in the early days, but now it is generally used with special motion control module. Such as a single-axis or multi-axis position control module that can drive a stepping motor or a servo motor. Almost all the products of major PLC manufacturers in the world have motion control functions, which are widely used in various machinery, machine tools, robots, elevators and other occasions.

4. Process control

Process control refers to the closed-loop control of temperature, pressure, flow and other analog quantities. As an industrial control computer, PLC can compile various control algorithms and complete closed-loop control. PID regulation is a widely used regulation method in general closed-loop control system. Large and medium-sized PLC has PID module, and many small PLCs also have this function module at present. Process control is widely used in metallurgy, chemical industry, heat treatment, boiler control and other occasions.

5. Data processing

Modern PLC has the functions of mathematical operation (including matrix operation, function operation and logic operation), data transmission, data conversion, sorting, table lookup, bit operation and so on, which can complete data collection, analysis and processing. These data can be compared with the reference values stored in the memory to complete some control operations, and can also be transmitted to other intelligent devices by using communication functions, or printed and made into tables. Data processing is generally used in large-scale control systems, such as unmanned flexible manufacturing systems; It can also be used in process control systems, such as some large-scale control systems in papermaking, metallurgy, food and other industries.

6. Communications and networks

PLC communication includes communication between PLCs and communication between PLCs and other intelligent devices. With the development of computer control and the rapid development of factory automation network, all PLC manufacturers attach great importance to the communication function of PLC and have launched their own network systems. The newly produced PLC has communication interface, which makes communication very convenient.